I am specifically arguing that we do not (should not) accept a priori the premise that surveillance is not necessarily bad.
To do so is to capitulate the entire argument against surveillance, and reduce our fight for privacy to nothing more than weighing lesser evils.
Is it? Please demonstrate it by listing terrorist incidents prevented or active terrorists caught due to surveillance other than narrowly-targeted police investigation, or military action in an active combat zone.
To qualify, the use of broad surveillance should be a necessary component of the investigation, i.e. the investigation would not have started or reached the conclusion it did without it. If some of these exist but they're all classified, that's problematic from the perspective of democracy because it prevents the public from making an informed decision about their merit.
It is if you're not going to accept a priori the claim that surveillance can be justified. If you need to have it demonstrated that surveillance can be justified, the only possible grounds for such a demonstration is to show the people the benefits--the actual harms that surveillance has prevented. If we the people can't see those benefits, how can we possibly judge whether or not surveillance can be justified?
In other words, the government of any free society is in a kind of Catch-22 position with regard to surveillance: it can't be justified to the people without revealing that it's happening and what it's discovering, but revealing those things destroys the usefulness of the surveillance. The only choices are to not permit the surveillance at all, or to accept an unavoidable loss of freedom--as a citizen, you will never be able to know whether the surveillance your government is conducting is justified. You just have to accept it.
"It's too secret to tell the public in broad terms a decade after the investigation is over" strikes me as incompatible with democracy. Questionably-legal surveillance also strikes me as incompatible with democracy outside of short-term use in exceptional emergency conditions, which should be disclosed to the public once the emergency is over.
Fill in the blank, masters. Maximize our security.
If you are interested in negotiating for minor concessions with entities who have demonstrated a willingness to work outside the law (and write new laws where needed), then your pragmatism will boil you slowly.